For example, a conventional voltage regulator comprises an input terminal to receive a supply voltage, an output terminal to provide an output voltage, and a first transistor which couples the input terminal of the voltage regulator to the output terminal of the voltage regulator. Furthermore, the voltage regulator comprises a second transistor, wherein the first and the second transistors form a current mirror structure. Further on, the voltage regulator comprises a control node which is coupled to the input terminal of the voltage regulator via the second transistor and which is coupled to the output terminal of the voltage regulator via a feedback circuit forming a control loop. The feedback circuit may comprise a feedback amplifier.
A conventional method for voltage regulation comprises supplying a supply voltage to a first and a second current path and providing an output voltage at the first current path. Further on, such method comprises mirroring a first current in the first current path to a second current in the second current path and controlling the second current path depending on the output voltage by a control loop. For example, the second current path is controlled depending on a comparison of a feedback voltage derived from the output voltage to a feedback reference voltage.
Such a voltage regulator is shown for example in “A Low Noise, High Power Supply Rejection Low Dropout Regulator for Wireless System-on-Chip Applications”, S. K. Hoon et al., Proceedings of the IEEE Custom Integrated Circuit Conference, CICC05, San Jose, USA, pp. 759-762, September 2005. According to that document, the supply voltage is provided to a first terminal of the first transistor and to a first terminal of the second transistor. A second terminal of the second transistor is connected to the control node. The control node is coupled to a reference potential terminal via a third transistor. Since the control node is directly connected to a control terminal of the first transistor, a disturbance of the supply voltage has an influence on the output voltage. Furthermore, a current which flows through the third transistor also depends on a variation of the supply voltage.
The document “A Low-Voltage, Low Quiescent Current, Low Drop-Out Regulator”, G. A. Rincon-Mora, P. Allen, IEEE Journal of Solid-State Circuits, volume 33, no. 1, January 1998, pp. 36-44 shows a further power supply circuit having a first and a second transistor in a mirror configuration.